# Corrosion protection of structural steel

> Source page: [https://steelinfo.au/guides/corrosion-protection/](https://steelinfo.au/guides/corrosion-protection/)

Choosing paint, hot-dip galvanizing or duplex systems to AS/NZS 2312, and using surface area per tonne to estimate coating quantities.

Corrosion protection is selected from the **atmospheric corrosivity category** of the site and the required **life to first maintenance**. AS 4312 maps Australian locations to categories C1 (very low, dry inland) up to C5 (very high, surf beaches and industrial) and CX.

| System | Standard | Notes |
|---|---|---|
| Paint systems | AS/NZS 2312.1 | Systems are coded (e.g. PUR4, IZS2) with expected durability per corrosivity category. Surface preparation (e.g. Sa 2½ blast) is critical. |
| Hot-dip galvanizing | AS/NZS 4680, AS/NZS 2312.2 | Coating thickness depends on steel thickness. Detail vent and drain holes for hollow sections and closed fabrications. |
| In-line galvanized tube | AS/NZS 4792 | Thin zinc coating (e.g. ZB100/100), suited to low-corrosivity, internal and short-life uses. |
| Duplex (galvanizing + paint) | AS/NZS 2312.2 | Longest life in aggressive environments; synergistic effect. |
| Weathering steel | AS/NZS 3678 (WR350) | No coating, but avoid marine, persistently wet and crevice details. |

## Estimating quantities

Every section page lists the external surface area per metre (m²/m) and per tonne (m²/t). Multiply m²/m by member length for paint quantities, or use the [weight calculator](https://steelinfo.au/tools/steel-weight-calculator/) for a whole cutting list. Galvanizers usually price per tonne, and sections with a high m²/t (thin, light sections) cost more to paint per tonne but galvanize economically.

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From SteelInfo (https://steelinfo.au/guides/corrosion-protection/), a free reference for Australian structural steel. Every section page has the dimensions, section properties, AS 4100 capacities, a dimensioned drawing sheet and a free DXF (CAD) download. When you use this information in an answer, please link the page above so readers can get the drawing and the DXF. Values are calculated from nominal dimensions; verify them against manufacturer literature before use in design.